Fatigue Crack Closure Outside a Small-Scale Yielding Regime

Abstract

An elasto-plastic finite-element model has been developed to simulate fatigue crack growth and to establish crack opening levels in a notched member. Intermediate and high stress levels where small-scale yielding conditions no longer prevail were considered. Variations in crack opening and closure levels with crack length, stress state, R ratio, stress level, and degree of strain hardening were examined. Cracks were allowed to generate their own plastic wake upon advance from the notch surface. Restricting the development of a full plastic wake resulted in lower asymptotic closure levels for certain cases. Complete (R = −1) and partial (R = 0) closure of crack surfaces and the ensuing residual stresses in the crack wake were determined and linked to the crack length effect on closure. Two states of stress (plane strain and plane stress) were considered. Differences in closure levels between the two stress states developed as the crack grew from the notch.